An ideal LC circuit consists of a capacitor of capacitance \(C\) connected to an air-core inductor of self-inductance \(L\). The capacitor is initially charged, and an oscilloscope connected across the capacitor displays a sinusoidal voltage waveform of period \(T\). A ferromagnetic iron core of relative permeability \(\mu_r > 1\) is then fully inserted into the interior of the inductor coil. Which of the following correctly describes how the observed period of oscillation of the capacitor voltage changes, and provides the correct justification?